1. Field of the Invention
The present invention relates to a data processing circuit used for a data serial interface etc.
2. Description of the Related Art
As an interface for multimedia data transfer, an IEEE (The Institute of Electrical and Electronic Engineers) 1394 high performance serial bus which realizes high speed data transfer and real-time transfer has recently been standardized.
The data transfer by the IEEE 1394 serial interface includes the conventional asynchronous transfer for making requests, acknowledging requests, and acknowledging receipt and isochronous transfer wherein data is always sent once per 125 μs from a certain node.
In the IEEE 1394 serial interface having such two transfer modes, data is transferred in units of packets.
A data processing circuit used for the IEEE 1394 serial interface mainly comprises, as shown in FIG. 8, a physical layer circuit 1 for directly driving the IEEE 1394 serial bus BUS and a link layer circuit 2 for controlling data transfer of the physical layer circuit 1.
In the isochronous communication system in the above IEEE 1394 serial interface, for example as shown in FIG. 8, the link layer circuit 2 is connected to the IEEE 1394 serial bus BUS via a physical layer circuit 3.
The link layer circuit 2 is connected to an application 3, such as a moving picture coding experts group (MPEG) 2 transporter and a digital video cassette recorder (DVCR).
Summarizing the problem to be solved by the invention, data of, for example, digital satellite broadcasting is supplied to the link layer circuit 2 via a set-top box for digital satellite broadcasting. A plurality of channels are multiplexed in the data supplied to the set-top box.
A data processing circuit of the IEEE 1394 serial interface of the related art is not capable of selecting and outputting only a specified channel from the data comprised of a plurality of multiplexed channels.
Therefore, it has been necessary to provide an external circuit for selecting a channel for extracting data of a specified channel and inputting it to the link layer 2.
Also, when a specified channel is selected, there has been a desire in some cases to add information regarding the selected channel for transmission to the serial interface bus, however, the data processing circuit of the IEEE 1394 serial interface is not configured with the function of selecting a specified channel and adding information regarding the channel to the data of the selected channel.